1. Field of the Invention
The present invention generally relates to titanium aluminide for precision casting and a method of fabricating a certain product using such titanium aluminide, and more particularly to titanium aluminide containing Fe and V to demonstrate a high creep strength and a precision casting method taking advantage of such titanium aluminide.
2. Description of the Related Art
Titanium aluminide (TiAl alloy) possesses various advantages such as being lightweight, demonstrating satisfactory strength at elevated temperature and having decent rigidity. Therefore, the titanium aluminide is considered as a new favorable material for rotating parts of an aircraft engine and vehicle engine or the like, and there is an increasing tendency to put it to practical use.
Conventionally, Fe, V and B are added to TiAl alloy to fabricate a complicated product by precision casting. By applying an optimum heat treatment, TiAl alloy is also improved in room temperature ductility, workability and fabricability. These techniques and approaches are disclosed in, for example, Japanese Patent Application, Laid-Open Publication No. 8-311585. Another known titanium aluminide for precision casting is disclosed in, for instance, U.S. Pat. No. 5,296,055 issued to Matsuda, entitled "TITANIUM ALUMINIDES AND PRECISION CAST ARTICLES MADE THEREFROM".
However, studies of TiAl alloys are primarily focused on improvements of room temperature ductility so that developed TiAl alloys have relatively low creep strength. Particularly, the creep strength is not very good beyond 700.degree. C.
In order to raise the creep strength of TiAl alloys, there is known a method of adding a third element (Mo, Cr, W, Nb, Ta, etc.) in a TiAl mother alloy. This is called a third element addition method. Another known method is a method of controlling a structure in such a manner that a volumetric ratio of .gamma. phase (TiAl) is raised in a TiAl alloy ("structure-controlling method).
However, the third element addition method considerably deteriorates precision castability of TiAl alloy so that a complicated product cannot be moldable. The structure-controlling method causes the room temperature ductility of TiAl alloy to drop below 0.5% so that machinability is greatly degraded.